The invention relates to the field of electronic reproduction technology for single-color printing, and particularly relates to a method and an apparatus for producing color separations. What is meant by single-color printing is, for example, textile printing, decorative printing, or packaging printing.
The color application to the print medium in multi-color mixed printing occurs by means of superimposed printing of different proportions of the printing inks "yellow", "magenta", "cyan" and "black". However in single-color printing, each color to be printed is blended before the printing process and is then separately transferred to the print medium so that a corresponding color separation must be produced for every color of the pattern master.
Such a pattern master exhibits, for example, color tones with a graduated color distribution, i.e. with a differing color saturation and/or luminosity within the individual color tones. In this case, the color separations must indicate the topical distribution of the individual colors as well as indicate the shading (continuous tone) or graduated color distribution, i.e. the locally different strength of the color application.
An installation for producing color separations for single-color printing is already known from U.S. Pat. No. 4,261,011, incorporated herein by reference. Three primary measured color signals which represent the color components red, green, and blue of the scanned image points are obtained by means of point-wise and line-wise opto-electronic scanning of a pattern master. A brightness signal is acquired or generated from the measured color values in a progression signal generator for the shading of the colors or, in case the progression signal generator is a standard color computer for multi-color mixed printing, color separation signals are generated. Either the brightness signal or a color separation signal selected before the recording is employed as a recording signal for a color separation. A color recognition circuit having the measured color signals is pre-set for recognition of the individual master colors in the pattern master. The color recognition circuit supplies corresponding color recognition signals when the pre-set master colors are recognized during the scanning of the pattern master. The selected recording signal of the corresponding master color is always connected through to a write lamp of the recording element during the recording of the color separation of a selected master color as a function of the color recognition signal of the master color. This recording signal is connected through whenever the selected master color is recognized in the pattern master.
The write lamp--modulated in brightness by the recording signal--exposes a recording medium, for example a film, point-wise and line-wise. This recording medium represents the desired color separation after it is developed.
Given this method, the individual color tone distributions appear sharply delineated in the corresponding color separations so that the individual colors are printed exactly next to one another in the subsequent printing. This can be advantageous depending on the type of pattern masters, but can also occasionally lead to disturbing interruptions of the color transitions.